The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Conventional brake disks are primarily produced from gray cast iron (GG15, GG25) or nodular cast iron (cast iron with globular graphite: GGG60, GGG70) and machined in a cutting process by means of turning. Proposals to replace the heavy gray cast iron material with aluminum are known from the prior art. On account of the low density of aluminum, the weight of the brake disk can consequently be reduced by approximately 50%. Such a brake disk, however, has significant disadvantages. On the one hand, aluminum alloys, in contrast to gray cast iron material, do not have the necessary abrasion resistance, also the melting point of aluminum-cast iron alloys lies below 650° C. When performing brake tests, such as the so-called AMS (Automotor and Sport) test, however, during repeated braking maneuvers from a speed of 115 km/h to 0 km/h temperatures of above 750° C. were measured on the gray cast iron brake disk. On the other hand, aluminum alloys have a many-times higher heat conductivity compared with gray cast iron material and can therefore dissipate resulting friction heat more quickly to the ambient air.
Known as a possible solution in the prior art are aluminum alloys the melting point of which is increased on account of a high silicon content (so-called hypereutectic aluminum-silicon alloys). At the same time the increased silicon content in this case leads to an increased abrasion resistance.
Also described in the prior art is the use of aluminum materials which are produced by spray compaction of molten metals, wherein during a subsequent manufacture of a component by extrusion the improved mechanical and thermal properties are maintained (Peter Krug: “Spray compacted aluminum alloys—uncommon materials for demanding lightweight concepts”, Forging Journal September 2008, p. 34-36).
These aluminum materials (for example the commercially available DISPAL®-aluminum materials) are produced by means of the powder metallurgical process of spray compacting and have a content of up to 35% silicon. By the addition or silicon carbide in the powder metallurgical process the abrasion resistance can be further increased. Brake disks made from aluminum with reinforcing particles consisting of silicon carbide (Duralcan®) have already been used as cast aluminum brake disks. However, these disks have not been able to be established in the market on account of issues in the castability and high aftermachining costs.
Another approach, in which conventional aluminum-silicon brake disks are protected against abrasive wear by a coating consisting of hard metal (e.g. tungsten carbide-cobalt WC-Co), leads to high costs on account of the use of strategically vital tungsten carbide and the diamond tools which are required for an aftermachining.
Also described in the prior art are hybrid brake disks in which the so-called chamber consists of an aluminum-forged alloy or aluminum alloy and an abrasion-loaded friction surface of the brake disk consists of a cast gray cast iron material.
An example of another hybrid brake disk is known from CN 103939509 A. This patent application describes a friction pair consisting of an Al/SiC (aluminum/silicon carbide) and Cu/SiC (copper/silicon carbide) composite material for use for rail vehicles, and a production method for the Al/SiC-Cu/SiC friction pair. A compound which is formed from a silicon carbide-ceramic structure is embedded in the friction surface of the friction pair. A multiplicity of heat-dissipating ribs are arranged on the other side of the friction pair in a circumferential direction. Formed in the middle of each of the heat-dissipating ribs is a ventilation passage which extends through the brake disk. The silicon carbide-ceramic structure is embedded in the friction surface of a Cu/SiC brake lining. Grid-like, heat-dissipating cooling ribs are arranged on the other side of the Cu/SiC brake lining.
The method for producing the Al/SiC-Cu/SiC composite material friction pair comprises steps for producing the compound formed by the silicon carbide-ceramic structure, a pretreatment of the silicon carbide-ceramic structure, construction and production of a brake disk and a brake lining casting mold, casting of the brake disk and the brake lining at low pressure, carrying out a heat treatment of the brake disk and the brake lining, precision machining of the brake disk and the brake lining and storing of the finished product. In this case, the Al/SiC-Cu/SiC composite material friction pair is intended to be able to be easily produced, to have a low weight and high and stable friction coefficient, to have good heat conducting properties and a long service life and is intended to be suitable for existing rail vehicles.
Described in CN 104235237 A is a road vehicle brake disk made from a composite material built up from carborundum (silicon carbide)-foamed ceramic and aluminum alloys and a method for producing the road vehicle brake disk. The body of the reinforced aluminum alloy brake disk with a carborundum-foamed ceramic structure is produced from reinforced aluminum alloy materials such as an aluminum alloy or nano-ceramic particles or carbon nano-tubules. The carborundum-foamed ceramic structure is cast onto two symmetrical friction surfaces of the brake disk. Grooves for heat dissipation or axial holes can be formed on the friction surfaces.
A multiplicity of heat-dissipating cooling ribs are cast in the circumferential direction of the non-friction surfaces. Fastening holes are formed in the disk body. The production method includes steps for producing the carborundum-foamed ceramic structure, premachining of the ceramic structure, construction and production of a casting mold of the brake disk, low pressure casting of the brake disk, heat treatment of the brake disk, precision machining of the brake disk, and storing of the finished product.
For producing hybrid brake disks, the use of additive production methods such as 3D and laser deposition welding also come into consideration.
By means of 3-D printing, plastics, synthetic resins, ceramics and metals can be used as materials. For example, U.S. Pat. No. 9,144,940 B2 describes a method for printing a three-dimensional part and a support structure using an additive production system based on electrophotography. The method includes forming a backing layer of the support structure from a soluble auxiliary material, which contains a first and a second copolymer, using a first electrophotographic machine, and transferring the formed backing layer from the first electrophotographic machine onto a transfer medium.
Furthermore, CN 104404508 A describes a laser-based additive production method for producing a structural part from an aluminum alloy. The laser-based additive production method is characterized in that an autonomous argon protective device is positioned on a work table, a base material consisting of aluminum alloy is positioned in the autonomous argon protective device, ultra-pure argon gas is injected beforehand, wherein the oxygen content in the cavity is less than 70 μl/l, and a customized powder feed device is used to order to feed in aluminum, an iron-based alloy, the rare earth material La2O3 and other superfine metal powders which are uniformly mixed according to a specified mass ratio by the use of laser beams in a melting bath in order to thereby form a laser beam coating which is subjected to a metallurgical bonding with the base material. The numerically controlled working program then carries out the laser beam coating layer by layer for all the layers until finally a three-dimensional metal part has been produced. In this way, the high-performance, completely compact aluminum alloy structural part with a rapid solidification structure and a complex geometry can be produced. According to the description, the laser-based additive production method has low production costs, short production times, a high material usage and a stable performance and can quickly produce complicated components, significantly improve the strength properties of the aluminum alloy structural part and reduce structural defects, such as gas pores, cracks, residual stress, etc., in the alloy.
Korean Patent KR 101587411 B1 describes a heat treatment device for a 3D-metal printer and a method relating to this for the heat treatment of a structure. The heat treatment device comprises a 3D-metal printer, which stacks and processes a structure by the melting of metal powder by means of a laser, a main control part for controlling an operation of the 3D-metal printer and a heat treatment unit. The heat treatment unit carries out a heat treatment of each layer during the stacking. The heat treatment device therefore carries out a heat treatment of the structure and of its interior, which is required during the process of stacking and processing of the structure with the 3D-metal printer, by performing heat treatments on even layers.
Described in EP 0 833 698 B1 is a method for producing ceramic-metal structures in which is particularly provided a solution for producing a structure consisting of a non-wetting, liquefiable material, for example a liquefied metal such as aluminum, copper, magnesium, etc., on a solid substrate which is not wettable by the material.
Described in one embodiment is a method for producing a ceramic-metal band which for example can be used for lightweight automobile brakes. The method comprises the following steps:
depositing a layer of a non-wettable ceramic powder on a formed solid mold;
depositing a layer of a wettable powder on the layer of the non-wetting ceramic powder;
bringing a metal into contact with the layer of the wettable powder;
heating the metal to a temperature at which the metal exerts a capillary action between the particles of the layer of wettable powder and comes into contact with the layer of the non-wettable ceramic powder in order to form a metal-penetrated structure; and
cooling the metal-penetrated structure in order to solidify the metal and to form a ceramic-metal band on the solid mold.
On the evidence of the featured prior art, the field of hybrid brake disks offers more room for improvements with regard to temperature loadability, abrasion resistance, lower complexity of production, and design freedom.